The antigen-antibody reaction is the basis for all immunological test methods. Special proteins called antibodies are produced by an animal in response to the presence of an antigen, that is a foreign substance usually a protein, in the body fluids of the animal. This normal body response to a foreign protein has led to the development of a number of techniques which are used to diagnose various human and animal diseases or disorders. In vitro tests for the presence of a suspected antigen or antibody in a body fluid are carried out by adding the immunological counterpart to a vial of the body fluid, i.e., add antigen if the test is for the presence of antibody or add antibody if the test is for the presence of antigen. If the suspected protein is present, the resulting antigen-antibody reaction is generally manifested by precipitation or agglutination of the antigen-antibody complex.
In some instances the antigen-antibody complex is slow to form and the particles that are formed are too small to be observed with certainty. In such cases, detectability of the antigen-antibody reaction can be improved by utilizing a carrier. When the antigen or antibody is coated onto the surface of a carrier the reaction that occurs with the immunological counterpart produces a visible mass or agglutant. The proteinic antigen or antibody may be adsorbed onto the surface of carriers such as erythrocytes, bacterial cells, bentonite, polystyrene latex particles, anionic phenolic resins, or finely divided diazotized amino cellulose. It has been found, however, that chemical binding of the antigen or antibody molecule to the carrier is superior to physical adsorption. U.S. Pat. No. 3,857,931 teaches that proteinic antigens or antibodies can be chemically bound to a polymer latex carrier having surface carbonyl groups by an amide bond formed in the presence of a water-soluble carbodiimide coupling agent. U.S. Pat. No. 3,806,417 describes a method of bonding a protein to a carrier having an expoxide group. A disadvantage of this method is that the protein must first be reacted with a compound having both an epoxy and olefinic group. The resulting conjugate is the polymerized with another olefinic monomer and bis-olefinic crosslinking agent to form the carrier bound enzyme.
The following references describe methods of bonding a protein to a polymer having an epoxide group: U.S. Pat. Nos. 3,853,708; 3,841,970; 3,844,892 and 3,821,084. The techniques described in these references, however, would not be suitable for use with a latex system.